I hope you had an opportunity to get out and enjoy the mild temperatures we had this weekend. During my typical winter walks, I tend to walk rather quickly in an effort to build up some heat and keep warm. But this weekend’s weather afforded me the opportunity to slow down (without fear of freezing) and explore the tiny winter world of lichens, mosses and galls. One abandoned fence post I came across seemed to have an entire miniature world perched atop it. 

In my wanderings, I came across dozens of oak apple galls, one of the more common galls found on Cape Cod oak trees, but I also came across a smaller tree with a set of oddly shaped galls I had never seen before. The tree was a scrub oak (Quercus ilicifolia), also known as a bear oak due to the bear-like shape of its leaves (think: gummy bear shape). The gall, rather than being the size and shape of a golf-ball like the oak apple galls, was much smaller and tapered to a point at both ends. 

A “gall” is a general term for a plant deformity caused by an insect or a fungus.  Like the oak apple galls, the galls on this scrub oak were likely caused by gall wasps in the family Cynipidae. Female wasps will lay a single egg in the petiole of a developing leaf. Chemicals and hormones secreted by the egg cause the oak to produce the gall, likely in an attempt to isolate the source of irritation. The wasp larva can then feed on the gall tissue produced in reaction to these secretions, as well as find shelter and protection inside this structure that the oak has produced around it, until it matures. The small hole in this dried gall husk is likely were the fully developed wasp exited the gall. 

In my search to determine what species might have made this gall, I stumbled upon an old scan of an American Museum Journal from 1904 with an article titled Insect Galls of the Vicinity of New York, which contained an illustration of a scrub oak gall very similar to the one I found today. So perhaps my mystery gall was created by Amphibolips ilicifolia? 

Have you ever seen one of these galls? Do you know what insect made it? Do you have any recommendations for good gall identification resources?